janne.peltonen@helsinki.fi wrote:

Full_Name: Janne Peltonen Version: 2.4.44 OS: Red Hat Enterprise Linux 7 URL: https://www.openldap.org/lists/openldap-technical/201901/msg00038.html Submission from: (NULL) (2001:708:110:1820:3664:a9ff:fe04:7363)

Proxied BINDs on back-ldap sometimes create Start TLS failed errors on the connection from proxy to backend, and the client of the proxy receives the error 52. We had a look at the code, and it appears that in back-ldap/bind.c, the timeout argument of the function ldap_back_start_tls always ends up as zero, so the timeout tv.sec and tv.usec end up being set as 0 and 100000, respectively, by the macro LDAP_BACK_TV_SET defined in back-ldap/back-ldap.h. This means that the actual timeout waiting for starttls operation to complete will be 0.1 seconds, which is sometimes too little if there are latencies. We did a quick&dirty hack to just set tv.sec to 3 and tv.usec to 0, and were no longer able to get any Start TLS failed errors on the proxy bind.

We did find that the back-ldap has an "extended" timeout defined in back-ldap/config.c - except that is commented out as "not implemented". Seems to us that if that were implemented, you could set the timeout in your ldap database section by something like "timeout extended=" and then you could have a longer timeout.

Thanks for the report. Note that if you simply set a "timeout" with no specific qualifiers, it would have worked for you as well.

At this point, the "extended" timeout was meant for the other exops that back-ldap supports, e.g. whoami and passwordModify. Since 2.4 is feature frozen we are not going to implement the extended timeout feature here.

Instead, I've changed the start_tls code to use the "bind" timeout, since it will always be used as part of a bind operation anyway.

Steps to reproduce:

1. Configure an openldap proxy-backend pair, the proxy using the "ldap" database

and using ldap urls to connect to the backend (using ldaps urls might actually be a workaround). Configure the binds to be proxied to the backend, too. 2. Create a script that creates multiple - say, 200 - simultaneous connections to the proxy, using an ldaps url to connect to the proxy, and using the same DN to bind as. (We haven't tried to connect to the frontend using ldap+starttls, but I would suppose that would have a similar result, since the client establishes TLS anyway before trying to bind to the proxy.) 3. Observe some of the binds fail (we typically get 5-6 fails for 200 simultaneous connection), with the client of the proxy getting a "Server is unavailable: 52" type of error, and the proxy log containing lines such as "conn=7716 op=0 RESULT tag=97 err=52 text=Start TLS failed" after the BIND from the client.

Possible workaround: Configure the proxy to use ldaps urls to the backend.

Suggested fix: Implement the "extended" timeout type in back-ldap/config.c timeout_table, so that people can set the StartTLS timeout to a larger value than the default 0.1 seconds.

References: discussion thread on the OpenLDAP-Technical mailing list.